The invention relates to a rotary bearing, in particular for optical measuring technology, such as measuring the image fidelity of an optical element.
Rotary bearings are generally used for realizing complete revolutions. For this purpose, rolling-element or sliding bearings are generally used. However, for rotation of an object in small angular increments, for example in {fraction (1/10)} degree increments or even less, rolling-element or sliding bearings are only suitable with restrictions, or, owing to their shaping, are almost unsuitable. This applies for example to running accuracy, friction and freedom from backlash.
In optical measuring technology, for the testing of optical imaging systems, for example of a lens system, it is often required to compare the latter with a sample copy or an image grating in order to establisb the quality of the unit being tested. In particular in the case of photolithographic processes for producing integrated semiconductor circuits, the optical systems used for this purpose have to meet extremely high accuracy requirements. When testing for distortion, for example of a lens system, a groove grating for example is arranged on the inlet side of the unit being tested and is transilluminated. The light falls through the measuring grating and the lens system, the lens system producing an aerial image of this groove grating. This groove grating is then placed into a physical grating, it being attempted to make the two gratings coincide or congruent. This test may take place, for example, by using interferometric means or by the moire method. For this test, the unit being tested must be rotated correspondingly on its rest. The required rotational movements are, however, generally in the range of 10 millidegrees.
DE 30 20 022 A1 describes a method and a device for testing optical imaging systems in which an original sample is compared with a sample copy produced by the imaging system to be tested. Indications as to how in constructional terms the unit being tested or from it the original grating and grating copy are to be made to coincide are not disclosed in this document.
The present invention is based on the object of providing a rotary bearing of the type mentioned at the beginning which is particularly suitable for rotation in very small angular increments, in particular for optical measuring technology, to be precise in particular with regard to a simple construction, accuracy and low friction.
This object is achieved according to the invention.
The rotary bearing according to the invention represents by virtue of its construction an adjusting unit which manages with few components and, in addition, has great rigidity. The arrangement of the outer mounting part and inner bearing part in one plane with the articulated joints lying in between has the effect that the rotational principle is two-dimensional, while the overall height represents a measure of the rigidity of the bearing in the direction of the axis of rotation. The properties of this bearing are consequently determined by the choice of the geometry and nature of the material. In this way, very great axial rigidity can be achieved, while the tangential rigidity is very low.
According to the invention, the inner bearing part is adjusted with respect to the outer mounting part, which is arranged such that it is fixed. The adjusting movement is passed on via the segments from which the inner bearing part is formed to a drive output part, which is respectively connected to the individual segments via resilient articulated joints, in such a way that a pure rotation of the drive output part is obtained. The optical element to be measured, for example a lens system, is placed onto the drive output part, unless the drive output part is already the optical element to be measured.
If, in a very advantageous refinement of the invention, it is provided that the outer mounting part and the inner bearing part are formed in one piece and are interconnected by solid-state articulated joints, a further component is saved. At the same time, freedom from backlash is obtained in this way. In addition, it is possible to dispense with additives for possible emergency running properties or minimizing friction.
Since, according to the invention, the bearing comprises only solid-state articulated joints with codirectional axes of rotation, interference with other degrees of freedom, i.e. corresponding effects on axes other than the intended axis of rotation, is ruled out. The adjusting range of the bearing is determined by the diameter ratio of the outer mounting part and inner bearing part as well as the elastic properties of the material.
In a very advantageous refinement of the invention, it is provided that each segment of the inner bearing part is connected to the outer mounting part via two articulated joints in each case, in such a way that a parallelogram-like displacement of each segment with respect to the outer mounting part is obtained.
The parallelogram-like displacement of the segments of the inner bearing part with respect to the outer mounting part according to the invention produces for the drive output part, which is connected to the segments via the resilient articulated joints, merely a rotation about the center of the bearing, while the movement of the connected resilient articulated joints compensates for the radial and tangential translation of the segments. In this case, the coupling of the individual inner ring segments may take place via two solid-state articulated joints, the common joining point of which represents the drive output.
The coupling according to the invention with the parallelogram-like displacement has the further advantage that the resulting radial movement of the segments is in a strict mathematical relationship with the rotation produced, so that it can be used as a measuring distance for a measuring sensor for measuring the rotational movement. In addition to the radial movement of the segments in relation to one another, a tangential movement of the segments also arises on the basis of the parallelogram-like displacement, whereby the distances between the individual segments also change.